Effect of Oceanographic Environments on Sexual Maturation, Salinity Tolerance, and Vasotocin Gene Expression in Homing Chum Salmon

Saito, Daisuke; Ota, Yuki; Hiraoka, Shûichi; Hyodo, Susumu; Ando, Hironori; Urano, Akihisa

doi:10.2108/zsj.18.389

Cited by 18 publications

(12 citation statements)

References 19 publications

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“…In pre-spawning chum salmon, the amounts of mRNAs encoding two VT precursors in the forebrains of females similarly decreased during upstream migration to both the long Ishikari river (Hiraoka et al, 1997) and the short Otsuchi river (Hiraoka et al, 1996;Saito et al, 2001). …”

Section: -1-1 Changes In Vt Gene Expression During Upstream Migrationmentioning

confidence: 96%

“…The amounts of VT mRNAs in the forebrains increased in the males, but decreased in the females coincidently with the loss of salinity tolerance in SW (Hiraoka et al, 1996;Saito et al, 2001). Such changes were obvious in pre-spawning chum salmon in 1994 when the warm current (Kuroshio) was dominant in the Sanriku coast and the homing fish in the Ostuch Bay completed final maturation, while not in 1995 when the cold current (Oyashio) dominated and the fish were not fully matured (Saito et al, 2001). These facts indicate that the salt and water balance in homing salmon depends on sexual maturation, which is under influence of environmental factors.…”

Section: -1-3 Salinity Tolerancementioning

confidence: 98%

Section: -1-3 Salinity Tolerancementioning

confidence: 99%

“…The plasma levels of Na + gradually elevated within a few days, when pre-spawning chum salmon in the Otsuchi Bay were retained in SW, followed by high mortality (Hirano et al, 1990;Saito et al, 2001). The amounts of VT mRNAs in the forebrains increased in the males, but decreased in the females coincidently with the loss of salinity tolerance in SW (Hiraoka et al, 1996;Saito et al, 2001). Such changes were obvious in pre-spawning chum salmon in 1994 when the warm current (Kuroshio) was dominant in the Sanriku coast and the homing fish in the Ostuch Bay completed final maturation, while not in 1995 when the cold current (Oyashio) dominated and the fish were not fully matured (Saito et al, 2001).…”

Section: -1-3 Salinity Tolerancementioning

confidence: 99%

“…In pre-spawning chum salmon, salt and water homeostasis, and gonadal maturation are highly influenced by year-to-year variation of oceanic environments, such as ambient water temperature and the distribution of cold current ( Saito et al, 2001;Onuma et al, 2003a).…”

Section: Introductionmentioning

confidence: 99%

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Expression of hormone genes and osmoregulation in homing chum salmon: A minireview

Makino

Onuma

Kitahashi

et al. 2007

General and Comparative Endocrinology

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Pacific salmon migrate from ocean through the natal river for spawning. Information on expression of genes encoding osmoregulatory hormones and migratory behavior is important for understanding of molecular events that underlie osmoregulation of homing salmon. In the present article, regulation of gene expression for osmoregulatory hormones in pre-spawning salmon was briefly reviewed with special reference to neurohypophysial hormone, vasotocin (VT), and pituitary hormones, growth hormone (GH) and prolactin (PRL).Thereafter, we introduced recent data on migratory behavior from SW to FW environment.In pre-spawning chum salmon, the hypothalamic VT mRNA levels increased in the males, while decreased in the females with loss of salinity tolerance when they were kept in SW.The amounts of GH mRNA in the pituitary decreased during ocean migration prior to entrance into FW. Hypo-osmotic stimulation by SW-to-FW transfer did not significantly affect the amount of PRL mRNA, but it was elevated in both SW and FW environments along with progress in final maturation. Behaviorally, homing chum salmon continued vertical movement between SW and FW layers in the mouth of the natal river for about 12 hours prior to upstream migration. Pre-spawning chum salmon in an aquarium, which allowed fish free access to SW and FW, showed that individuals with the lower plasma testosterone (T) and higher estradiol-17β (E2) levels spent longer time in FW when compared with the SW fish.Taken together, neuroendocrine mechanisms that underlie salt and water homeostasis and migratory behavior from SW to FW may be under the control of the hypothalamus-pituitary -gonadal axis in pre-spawning salmon.

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Section: -1-1 Changes In Vt Gene Expression During Upstream Migrationmentioning

confidence: 96%

Section: -1-3 Salinity Tolerancementioning

confidence: 98%

Section: -1-3 Salinity Tolerancementioning

confidence: 99%

Section: -1-3 Salinity Tolerancementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Expression of hormone genes and osmoregulation in homing chum salmon: A minireview

Makino

Onuma

Kitahashi

et al. 2007

General and Comparative Endocrinology

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Elevation of gene expression for salmon gonadotropin-releasing hormone in discrete brain loci of prespawning chum salmon during upstream migration

et al. 2005

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Our previous studies suggested that salmon gonadotropin-releasing hormone (sGnRH) neurons regulate both final maturation and migratory behavior in homing salmonids. Activation of sGnRH neurons can occur during upstream migration. We therefore examined expression of genes encoding the precursors of sGnRH, sGnRH-I, and sGnRH-II, in discrete forebrain loci of prespawning chum salmon, Oncorhynchus keta. Fish were captured from 1997 through 1999 along their homing pathway: coastal areas, a midway of the river, 4 km downstream of the natal hatchery, and the hatchery. Amounts of sGnRH mRNAs in fresh frozen sections including the olfactory bulb (OB), terminal nerve (TN), ventral telencephalon (VT), nucleus preopticus parvocellularis anterioris (PPa), and nucleus preopticus magnocellularis (PM) were determined by quantitative real-time polymerase chain reactions. The amounts of sGnRH-II mRNA were higher than those of sGnRH-I mRNA, while they showed similar changes during upstream migration. In the OB and TN, the amounts of sGnRH mRNAs elevated from the coast to the natal hatchery. In the VT and PPa, they elevated along with the progress of final maturation. Such elevation was also observed in the rostroventral, middle, and dorsocaudal parts of the PM. The amounts of gonadotropin IIbeta and somatolactin mRNAs in the pituitary also increased consistently with the elevation of gene expression for sGnRH. These results, in combination with lines of previous evidence, indicate that sGnRH neurons are activated in almost all the forebrain loci during the last phases of spawning migration, resulting in coordination of final gonadal maturation and migratory behavior to the spawning ground.

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Quantitative analyses of the levels of hormonal mRNAs in the salmon neuroendocrine system

Urano

Ando

2003

Aquatic Genomics

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Effect of Oceanographic Environments on Sexual Maturation, Salinity Tolerance, and Vasotocin Gene Expression in Homing Chum Salmon

Cited by 18 publications

References 19 publications

Expression of hormone genes and osmoregulation in homing chum salmon: A minireview

Expression of hormone genes and osmoregulation in homing chum salmon: A minireview

Elevation of gene expression for salmon gonadotropin-releasing hormone in discrete brain loci of prespawning chum salmon during upstream migration

Quantitative analyses of the levels of hormonal mRNAs in the salmon neuroendocrine system

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